Green roofs have been around for thousands of years and precursors to the modern green roof, such as sod roofs, have been used in many cultures for centuries.

The modern day green roof uses modern technology such as root barriers, drainage systems and lightweight growing media which allows healthy growing environments at much lighter weights. Lightweight green roofs allow systems to be installed on roofs which normally would not be able to sustain heavy loads, as is the case with Stokes Hall. While some roofs can withstand weights up to 60+ lbs per square foot, Stokes has only been rated for 21 lbs fully saturated.

The system selected for Stokes Hall is an Aromatic Garden “Roofmeadow” system. Because the “soil” or growing media is only 3-4” thick, drought tolerant plants were selected, namely sedums. Sedums will withstand long periods of drought and won’t need supplemental irrigation.

The photograph to the right is Friends Center at 15th and Cherry streets in Philadelphia. Their system, which is the same as ours, is two years old. This roof is in full bloom.*